Complex phosphates

ABSTRACT

Solid water-soluble aluminum phosphate complexes and binder composition which dissolve in water to give solutions containing aluminum ions and orthophosphate ions in such proportions as to provide an Al:P ratio of substantially 1:1 together with the anions of a carboxylic acid or a mineral oxyacid.

United States Patent AU 115 EX Birchall et al.

COMPLEX PHOSPHATES Inventors: James Derek Birchall; John Edward Cassidy; Nicholas Rolfe; Clifford 'Granville Miles, all of Runcom,

England Assignee: Imperial Chemical Industries Limited, London, England Filed: Oct. 12, 1972 Appl. No.: 296,985

Foreign Application Priority Data Oct. 19, 1971 United Kingdom 48576/71 June 8, 1972 United Kingdom 26803/72 US. Cl. 106/65; 106/55; 106/85 Int. Cl C04b 35/02 Field of Search 106/65, 85, 188.5, 55

[ 1 Aug. 12, 1975 Primary Examiner-J. Poer Attorney, Agent, or F irmCushman, Darby & Cushman 5 7 1 ABSTRACT Solid water-soluble aluminum phosphate complexes and binder composition which dissolve in water to give solutions containing aluminum ions and orthophosphate ions in such proportions as to provide an AlzP ratio of substantially 1:1 together with the unions of a carboxylic acid or a mineral oxyacid.

11 Claims, No Drawings COMPLEX PHOSPHATES This invention relates to water-soluble solid aluminum phosphate complexes and binder compositions, and to solutions of aluminium phosphate and their use for binding refractory materials and coating surfaces.

The use of acid aluminium phosphates, for example Al(H PO and Al (HPO as refractory binders which can be cured by heat is well known. However, these acid binders suffer from the disadvantage that their cured forms can undergo several phase changes at relatively low temperatures, for example temperatures in the range 300 to 800C. These phase changes are undesirable as they tend to reduce the strength developed by the product on heating.

We have found that, surprisingly, an aqueous solution containing aluminium ions and orthophosphate ions in such proportions as to provide an Al:P ratio of substantially 1:] together with the anions of a carboxylic acid or a mineral oxyacid can be formed and is effective as a refractory binder which is less liable to the phase changes mentioned above.

Thus there is provided a method of binding refractory solids which comprises forming a slurry or paste containing the solids to be bound and an aqueous solution containing aluminium ions and orthophosphate ions in an Al:P ratio of substantially 1:1 and additionally the anions of a carboxylic acid or a mineral oxyacid, and curing" the phosphate binder.

Curing the phosphate binder involves removing at least a proportion of the additional anions present so rendering the aluminium phosphate insoluble. This Y may be effected by heating. The precise temperature is not critical although temperatures of 80C and more will generally be used. The exact temperature required in any particular case will depend upon the composition of the binder and especially the nature of the additional anions but, in most cases, we find that a temperature in the range 80 to 200C is sufficient, although higher temperatures may be used if desired.

Alternatively, the binder may be cured in the cold by the use of a setting agent which reacts with the additional acid anions present. Thus the setting agent should be basic, for example magnesium oxide. The use of a cold-setting binder is especially advantageous for the production of monolithic refractories, for example, castables" (produced by casting a slurry of the binder and a refractory material in a mould) and gunning mixes.

The binder solution contains aluminion ions and orthophosphate ions in such proportions as to provide an Al:P ratio of substantially 1:], that is l:O.8 to l:l.3,

preferably l:O.95 to 1:105

The anions of mineral oxyacids present may be, for example, nitrate anions or sulphate anions. When carboxylic acid anions are present, these are preferably the anions of polycarboxylic acids, for example citric acid and oxalic acid. If desired, a mixture of the anions of more than one acid may be used.

The acid anions should be present in an amount at least sufficient to render the aluminium orthophosphate readily soluble. The amount of acid anions required for this purpose will vary from acid to acid, and will depend on the precise ratio of Al:P present, but will generally be sufficient to provide an anionzAl ratio of at least 0.5:]. Increasing the proportion of the anion present at first increases the solubility of the aluminium phosphate. although after an anionzAl ratio of about l.2:l has been exceeded there is generally little further increase in solubility. Since increasing the proportion of anion present will tend to increase the corrosiveness of the binder, there is generally little point in using a solution having an anionzAl ratio of greater than l.2:l and we prefer that the anionzAl ratio be in the range 0.7:] to 1.2: l although solutions of higher anionzAl ratios, for example 4:l or 3: l may be used if desired.

The binder may be prepared in solution by the admixture of aluminium phosphate and the acid containing the desired anions, for example nitric acid, or by the admixture of phosphoric acid with the aluminium salt of the desired anion, for example, aluminium nitrate.

Alternatively an aluminium acid phosphate and an aluminium salt of the desired anion may be dissolved,in

water in the porportions required to provide an Al:P

ratio of substantially 1:1.

The binders of the present invention are also available in solid form. This in an important advantage since a solid binder is, in many cases, more convenient to store and transport than a binder solution. Thus our invention also provides a solid water-soluble aluminium phosphate binder which dissolves in water to form a so-' the acid anion and aluminium in an anionzAl ratio of i 0.5:] to l.2:l, preferably 0.7:1 to l.2:l.

The solid binders of the invention may be prepared by admixing (preferably grinding together) a solid aluminium acid phosphate and an aluminium salt of a min eral oxyacid or a carboxylic acid (or a mixture of two or more such salts) in appropriate proportions to provide the desired Al:P ratio of substantially lzl; for example, grinding together equimolar proportions of aluminium nitrate, Al(NO and aluminium acid phosphate, Al (HPO Alternatively, the solid binders may be prepared by isolation of a solid from the binder solution by, for example, spray-drying or crystallisation. Surprisingly, we have found that the components of the solid binder form a single complex salt containingchemically-bound water.

Thus, according to a further aspect of the invention there is provided a solid water-soluble complex phos phate of aluminium, containing Al:P in a ratio of substantially 1:1, and containing chemically-bound water and a chemically-bound anion of a carboxylic acid or mineral oxyacid.

The complex phosphates of the invention contain Al:P in a ratio of l:O.8 to l:l.3, preferably 1:0.95 to l 1.05. Examples of the acid anions which may be present in the complex include those given above for the binder solutions. The preferred complexes contain the anion and aluminium in a ratio of anion:Al of 0.8:1 to l.2:l, although complexes containing smaller or greater proportions of anions are also useful.

The solid complex phosphates may be prepared, as noted above, by making up a solution of the binder (which solution is believed to contain the complexes) and separating the solid complexes from the solution in known manner, for example by crystallisation or spraydrying. In some cases, for example in the case of the nitrate-containing complex, the complex may be prepared by passing a gaseous precursor of the anion (such as the anhydride of the corresponding acid) over solid aluminium phosphate trihydrate. For example, by passing nitrogen dioxide over aluminium phosphate trihydrate; it is not necessary to heat the reactants and, indeed, it is important that the temperature is not allowed to rise above the decomposition temperature of the complex, that is, about 80C. On dissolving in water, the complexes of the invention do, of course, provide binder solutions in accordance with the invention.

The binders of the present invention are especially useful for binding refractory materials, for example, silica, alumina, e.g. tabular alumina and bauxite; magnesium, calcium and titanium oxides; zinc and tin oxides; magnesite; mag-chrome grog; zirconium silicate, zirconia; zircon; aluminium silicates, e.g. sillimanite, andalusite, kyanite, mullite and mollochite; porcelain and china clays; carbides, e.g. silicon and tungsten carbide, nitrides, e.g. silicon and boron nitride; boron; asbestos; ferric oxide; chomium oxide; chromite; mica; aluminium phosphate; and mixtures thereof. If a basic refractory material is used, this may also as as a cold-setting agent for the binder.

The binder will generally. but not necessarily, be used in an amount of l to 25%, preferably 2 to by weight, calculated as the solid and based on the weight of material to be bound.

A convenient form for supplying the solid binders of the invention is as a dry mix with the refractory material to be bound. Thus, according to a further aspect of the invention we provide a solid mix comprising a refractory material (especially in granular and/or fibrous form) and a solid binder preferably in the form of a complex phosphate) in accordance with the invention. If desired, the solid mix may contain a setting agent (as hereinbefore described) for the binder.

The solid mixes of the present invention are useful as refractory mortars and, when they contain a coldsetting agent, for the production of refractory "castablesf.

The novel complexes and solutions of the invention,

by virtue of the fact that they are capable of decomposing to give aluminium phosphate, resemble the halogen-containing complex phosphates of aluminium disclosed in our UK. patent application No. 29862/69 (Dutch patent application No. 7,008,594). In that, and in subsequent patent applications, we have described the use of the halogen-containing complex phosphates I :in the binding of solids and the coating of surfaces with aluminium phosphate. In the processes of many of l. the production of fibres comprising aluminium phosphatezcoating substrates, for example of glass, carbon, ceramics or organic polymers with a film of aluminium phosphate as described in Dutch patent application No. 7,008,594. I

2. the coating of surfaces with aluminium phosphate; effects which may be achieved using the coatings on a variety of substrates and particular techniques of applying the coatings are described in Dutch patent application No. 7,116,975.

3. binding of graphite for example in the manner described in our Dutch patent application No. 7,1 16,931.

4. binding inorganic fibres into felted form, for example in the manner described in our Dutch patent application No. 7,1 16,974.

5. coating of strengthened glass, for example in the manner described in our Dutch patent application No. 7,111,112.

6. the preparation of high surface area aluminium phosphate gels by removal of the additional anions from the solution in a controlled mann r, for example by warming or by the addition or A. base. The resultant gels are useful as catalysts or catalyst supports in, for example, cracking reactions.

7. the coating of mould surfaces (especially moulds for casting metal or glass) in the manner described in our Dutch patent application No. 7,109,014.

8. binding refractory materials to produce casting moulds, for example in the manner described in our Dutch patent application No. 7,103,318.

The invention is illustrated but not limited by the following Examples in which all parts and percentages are by weight unless otherwise stated:

EXAMPLE 1 Aluminium nitrate (335g) was dissolved in water (1 litre) and 57 ml of 88% orthophosphoric acid were added. The solution was heated in a water bath to give a white water-soluble solid, which was found to have the following composition:

A] 12.3%; PO, 1 43.3%; HNO 2 22.2%; 14,0 22.5%

corresponding to a molecular ratio of:

NO; 0.77. H O 2.74

EXAMPLE 2 Aluminium phosphate trihydrate (3.6g) was placed in a 500 ml flask filled at room temperature and atmospheric pressure with nitrogen dioxide gas. The flask was shaken for 15 minutes during which time the temperature of the solid rose to 35C and then cooled down. The pressure in the flask fell by 16 mm Hg. The resultant product was a white free-flowing solid which was soluble in water and on analysis was shown to have the following composition:

A1: 13.5%; Po, 1 45.7%; N0 11.9%; H2O 36.8%

corresponding to a molecular ratio of:

Al l; P 0.96; N01: 0.52; H1O 4.08

The product was subjected to differential thermal analysis. Two main peaks were observed: a weak endothermic peak centred on 60 to 70C and a strong endothermic peak centred on 160 to 170C. The latter decomposition takes place over a fairly broad range of 125 to 275C.

EXAMPLE 3 312g of aluminium nitrate nonahydrate and 93g of 88% orthophosphoric acid were dissolved in 94 ml of distilled water. The resultant solution was spray-dried using a co-current spray-drier with the chamber at atmospheric pressure. The drying gas, which was air, had an inlet temperature of 170C and an outlet temperature of 80C.

The solid product formed formed was highly soluble in water and had the following analysis:

Al NO; P H O by weight 10.8 23.5 30.6 26.1 Proportion 1.00 l .04 0.94 3.6

The infra-red spectrum of the solid product was measured using a pellet formed by compressing a sample of the product with potassium bromide. The following absorptions were observed:

3400 cm very strong, broad 1630 cm" strong 1382 cm strong 1 130 cm" very strong, broad 925 cm medium 825 cm weak 530 cm medium The absorptions at 3400 cm and 1630 cm are characteristic of water; the absorption at 1130 cm and 925 cm are characteristic of phosphate; the the absorptions at 1382 cm and 825 cm are characteristic of nitrate.

EXAMPLE 4 An aqueous solution of aluminium nitrate nonahydrate (2410g) and 88% orthophosphoric acid (615g) was prepared. The resulting solution contained approximately 40% by weight of Al( NO and H PO taken together.

The solution was spray-dried as in Example 3 at an inlet temperature of 235240C and an outlet temperature of 85-90C. The product, which was highly soluble in water, had the following analysis:

A] NO, P0 H O by weight 12.1 25.7 36.5 25.3

proportion 1.00 0.91 0.84 3.]

EXAMPLE 5 An aqueous solution of aluminium nitrate/phosphoric acid having the analysis:

Al P 4.5 5.2

% by weight was made up and spray-dried as described in Example 3. The inlet temperature was 196C and the outlet temperature was 81C. A water-soluble white solid having the following analysis was produced:

Al NO; P0 H O by weight 12.1 21.7 42.4 23.8 proportion 1.00 0.78 1.00 3.0

EXAMPLE 6 A sample of spray-dried complex aluminium phosphate containing nitrate anions and chemically-bound water and having the following analysis:

% by weight 21.6

was used in the preparation of a mortar having the following formulation:

Percentage Parts (based on total solids) 325 mesh calcined 990 33 alumina 60 mesh* calcined 1665 55.5

alumina I Hywhite alumina clay 4 Complex phosphate 225 7.5 Water 350 l 1.6

(Brit'sh Standard sicvc sizes) Temperature (C) Modulus of rupture (Kg/cm Room temperature 392 200 282 400 3 l 2 600 339 800 283 1000 294 [200 67.5 1300" 3 l .6 1400 19. 1

EXAMPLE 7 210g (1 mol) of citric acid monohydrate were dissolved in 144g of cold water. The solution was stirred and 176g 1 mol) of aluminium orthophosphate trihydrate were added. A viscous clear solution was obtained after stirring for 8 hours. This solution could be diluted without causing any precipitation.

Using this solution as the binder, ceramic test pieces were prepared using the following formulation:

Refractory Mix Tabular alumina, grade 325 33l3 Tabular alumina. grade 28-48 33l3 Tabular alumina. grade 8-14 33/3 -Continued Refractory Mix Citric acid/AlPO, Solution 7.5 Water 6 All the constituents were mixed together thoroughly and poured into 4 inch long by 1% inch cross-section moulds. They were allowed to dry at room temperature for several days. and then dried at l C for at least 2 days before being fired at 1000C for 1 hour.

The modulus for rupture for this ceramic mix was found to be 637 lb ft/in EXAMPLE 8 63g ((2 mol) of oxalic acid dihydrate were dissolved in' 195g of water at 55C. The solution was stirred and 88g (1i mol) of aluminium orthophosphate trihydrate were added. A clear solution was formed, which was used to prepare ceramic test pieces of the following formulation.

Refractory Mix Tabular alumina, grade 325 33'l3 Tabular alumina, grade 28-48 33'l3 Tabular alumina, grade 8-14 33 /3 Oxalic acid/AIPO solution 10 All the constituents were mixed together thoroughly and poured into 4 inch long by /2 inch cross-section moulds. They were allowed to dry at room temperature for several days, and then at l 10C for 2 days before being fired at 1000C for 1 hour.

The modulus of rupture for this ceramic mix was found to be 1024 lb ft/in EXAMPLE 9 Refractory Mix Tabular alumina. grade -325 33'l3 Tabular alumina. grade 28-48 33'/3 Tabular alumina. grade 8-14 33l3 Sulphosalicylic acid/ AlPO, solution 10 The constituents were mixed together thoroughly and poured into 4 inch long X 9% inch cross-section moulds. They were allowed to dry at room temperature for several days, and then dried at 1 10C for at least 2 days before being fired at 1200C for 1 hour.

The modulus of rupture for this ceramix mix was found to be 1 l 19 lb ft/in".

EXAMPLE 10 176g 1 mol) of aluminium orthophosphate trihydrate were added, with stirring, to 90g of concentrated nitric acid (this amount equivalent to 1 mol of HNO Addition of the aluminium phosphate caused the mix to become very sticky and difficult to stir. When this occurred small volumes of water were added. The final mix, containing 300g of water, was then warmed up to C to give a clear solution.

This solution was used as the binder in pressed ceramic specimens prepared from the following formulation:

Tabular alumina. grade 325 33'/3 parts Tabular alumina, grade 28-48 33% parts Tabular alumina. grade 8-14 33l3 pans Binder solution as above 12 parts The above constituents were thoroughly mixed and then left to dry for 1 hour to remove excess moisture. 1 inch diameter cylindrical specimens were pressed in moulds at a pressure of 3 tons. The specimens were dried for 16 hours at C and then fired at 1400C for 1 hour. The compressive strength of the specimens was found to be 2,510 lb/sq.in.

What we claimed is:

1. A method of binding refractory solids which comprises forming a slurry or paste containing the solids to be bound and an aqueous solution containing aluminium ions and orthophosphate ions in an Al:P ratio of substantially 1:1 and additionally the anions of a carboxylic acid or a mineral oxyacid in a ratio of additional anion: aluminium ions in the range of 0.5:1 to 4: 1, the aqueous solution containing from 1 to 25% of solids by weight of the refractory solids to be bound, and curing the phosphate binder.

2. A method as claimed in claim 1 wherein the solution contains aluminium and phosphorus in a ratio of 1:095 to 1:105.

3. A method as claimed in claim 1 wherein the additional anions in the solution are nitrate anions.

4. A method as claimed in claim 1 wherein the ratio of additional anions to aluminium ions in the solution is in the range 0.7:1 to 12:1.

5. A method as claimed in claim 1 wherein a coldsetting agent for the phosphate binder is included in the slurry or paste formed.

6. A method as claimed in claim 1 wherein the binder is cured by heating to a temperature of at least 80C.

7. A solid mix comprising a refractorymaterial and from 1 to 25%, based on the weight of the refractory material, of a solid water-soluble aluminium phosphate binder which is capable of dissolving in water to form a solution containing aluminium ions, orthophosphate ions and additionally the anions of a carboxylic acid or a mineral oxyacid, said ions being present in the solution in such proportions as to provide an Al:P ratio of substantially 1:1 and an additional anionzaluminium ion ratio in the range 0.5:1 to 4:1.

8. A solid mix comprising a solid water-soluble aluminium phosphate binder and a cold-setting agent therefor, the binder being capable of dissolving in water to form a solution containing aluminium ions, orthophosphate ions and additionally the anions of a carboxylic acid or a mineral oxyacid said ions being present in the solution in such proportions as to provide an Al:P ratio of substantially 1:1 and an additional anion- :aluminium ion ratio in the range 0.5:1 to 4:1.

9. A method as claimed in claim 1 wherein the additional anionzAl ratio is in the range 0.5:1 to 1.2:].

10. A method as claimed in claim 1 wherein the additional anionzAl ratio is at least 0.7.

11. A method as claimed in claim 1 where the solution is prepared by dissolving in water solid watersoluble complex phosphate of aluminium, containing Al:P in a ratio of substantially 1:1, and containing chemically-bound water and a chemically-bound anion of a carboxylic acid or mineral oxyacid. 

1. A METHOD OF BINDING REFACTORY SOLIDS WHICH COMPRISES FORMING A SLURRY OR PASTE CONTAINING THE SOLIDS TO BE BOUND AND AN AQUEOUS SOLUTION CONTAINING ALUMINUM IONS AND ORTHOPHOSPHATE IONS IN AN AL:P RATIO OF SUBSTANTIALLY 1:1 AND ADDITIONALLY THE ANIONS OF A CARBOXYLIC ACID OR A MINERAL OXYACID IN A RATIO OF ADDITIONAL ANION: ALUMINIUM IONS IN THE RANGE OF 0.5 TO 4.1, THE AQUEOUS SOLUTION CONTAINING FROM 1 TO 25% OF SOLIDS BY WEGHT OF THE REFRACTORY SOLIDS TO BE BOUND, AND CURING THE POSPHATE BINDER.
 2. A method as claimed in claim 1 wherein the solution contains aluminium and phosphorus in a ratio of 1:0.95 to 1:1.05.
 3. A method as claimed in claim 1 wherein the additional anions in the solution are nitrate anions.
 4. A method as claimed in claim 1 wherein the ratio of additional anions to aluminium ions in the solution is in the range 0.7:1 to 1.2:1.
 5. A method as claimed in claim 1 wherein a cold-setting agent for the phosphate binder is included in the slurry or paste formed.
 6. A method as claimed in claim 1 wherein the binder is cured by heating to a temperature of at least 80*C.
 7. A solid mix comprising a refractory material and from 1 to 25%, based on the weight of the refractory material, of a solid water-soluble aluminium phosphate binder which is capable of dissolving in water to form a solution containing aluminium ions, orthophosphate ions and additionally the anions of a carboxylic acid or a mineral oxyacid, said ions being present in the solution in such proportions as to provide an Al:P ratio of substantially 1:1 and an additional anion:aluminium ion ratio in the range 0.5:1 to 4:1.
 8. A solid mix comprising a solid water-soluble aluminium phosphate binder and a cold-setting agent therefor, the binder being capable of dissolving in water to form a solution containing aluminium ions, orthophosphate ions and additionally the anions of a carboxylic acid or a mineral oxyacid said ions being present in the solution in such proportions as to provide an Al:P ratio of substantially 1:1 and an additional anion: aluminium ion ratio in the range 0.5:1 to 4:1.
 9. A method as claimed in claim 1 wherein the additional anion: Al ratio is in the range 0.5:1 to 1.2:1.
 10. A method as claimed in claim 1 wherein the additional anion: Al ratio is at least 0.7.
 11. A method as claimed in claim 1 where the solution is prepared by dissolving in water solid water-soluble complex phosphate of aluminium, containing Al:P in a ratio of substantially 1:1, and containing chemically-bound water and a chemically-bound anion of a carboxylic acid or mineral oxyacid. 